1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic recording medium having a recording layer formed in a concavo-convex pattern.
2. Description of the Related Art
Conventional magnetic recording media such as hard disks have been significantly improved in areal density, e.g., by employing finer magnetic grains or alternative materials for the recording layer(s) and by advanced microprocessing of magnetic heads. Although further improvements in areal density are still being sought, these conventional approaches to the improvement of areal density have already reached their limits due to several problems that have arisen. These problems include the limited accuracy of microprocessing of magnetic heads, erroneous recording of information on tracks adjacent to the target track due to spread of a recording magnetic field produced by the magnetic head, and crosstalk during reproducing operations.
As candidate magnetic recoding media that could enable further improvements in areal density, discrete track media or patterned media have been suggested which have a recording layer(s) formed in a concavo-convex pattern and have recording elements formed as the convex portion of the concavo-convex pattern. On the other hand, for magnetic recording media such as hard disks, the flatness of the surface(s) thereof is important in order to stabilize the flying height of the head and thereby provide good recording/reproducing properties. In this context, use of filling material has been suggested to fill the concave portions between the recording elements to thereby flatten the top surfaces of the recording elements and filling materials (e.g., see Japanese Patent Laid-Open Publication No. Hei 9-97419).
Dry etching, for example, can be utilized to form the recording layer in a concavo-convex pattern. There are several techniques available to fill the concave portion with a filling material and flatten the top surfaces of the recording element and the filling material, such as sputtering, CVD (Chemical Vapor Deposition), and IBD (Ion Beam Deposition). These deposition techniques can be used to deposit the filling material on the concavo-convex patterned recording layer to fill the concave portions between the recording elements. Then, an excess part of filling material deposited above the top surface of the recording elements (the surface opposite to the substrate) may be removed by dry etching.
To provide good magnetic properties for the recording layer, the excess part of the filling material is preferably completely removed but the top surface of the recording element is not processed. That is, it is preferable to control the dry etching in the flattening step so that the endpoint of the etching is flush with the top surface of the recording element.
In the case of dry etching, a component of the recording element removed from and flying off the workpiece can be detected by secondary-ion mass spectrometry (SIMS) or quadrupole mass spectrometry (QMS). The etching can thus be stopped upon detecting the component of the recording element, thereby keeping the extent of variation in the etching endpoint to within several nanometers of the top surface of the recording element.
However, in order to detect a component of the recording element by secondary-ion mass spectrometry or quadrupole mass spectrometry, it is necessary to etch not only an excess part of filling material but also the recording element. Accordingly, a several-nanometer portion near the upper portion of the recording elements will be unavoidably etched, causing degradation in its magnetic property.
In this context, a technique is known in the field of semiconductors for depositing a detection material over the corresponding portions of the recording elements that are to be protected against etching, and detecting a component of the detection material, thereby stopping the etching (e.g., see Japanese Patent Laid-Open Publication No. 2003-078185).
This technique can also be utilized in the field of magnetic recording media to deposit a detection material on a concavo-convex patterned recording layer. Immediately after etching reaches the detection material and a component removed from and flying off the detection material starts to be detected, or alternatively, immediately after the component of the detection material once detected has disappeared, the etching may be stopped. This should allow for removal of the excess part of filling material without etching of the recording elements.
However, in the period immediately after the detection material has first started to be scattered, only a small amount of a component flying from the detection material is available. Thus, the secondary-ion mass spectrometry or quadrupole mass spectrometry sometimes cannot readily detect the exact point in time at which the etching has reached the detection material because the difference between noise and data indicative of the component of the detection material starting to be detected cannot be clearly is known.
Conversely, it is relatively easy to determine that the detection material once detected has substantially disappeared. However, the secondary-ion mass spectrometry and quadrupole mass spectrometry are intended to detect a component removed from and flying off the detection material. Thus, there will be a time lag between the point in time at which the detection material has actually been completely removed from the workpiece and the point in time at which the detection material is determined to have disappeared.
Accordingly, when the etching is stopped immediately after the detection material is determined to have disappeared, the detection material may have actually already been completely removed from the workpiece and the etching has proceeded further to etch the recording elements.
Furthermore, when the recording elements are etched, the filling material that fills the concave portions between the recording elements is also etched. Since the recording element and the filling material are formed of different materials and thus have different etching rates in general, the filling material in the concave portion may be etched further in conjunction with the recording element, thereby causing a several-nanometer step height between the top surface of the recording elements and the top surface of the filling material. Since discrete track media or patterned media of high areal densities are expected to have a flying height of the head as small as about 5 to 15 nm, even a several-nanometer step height could cause a problem such as a head crash. Incidentally, such a several-nanometer step height would also be produced in semiconductor manufacturing processes. However, semiconductors would never be subjected to such problems as head crashes and thus several-nanometer step heights are not generally problematic for them.